Method for dewaxing hydrocarbon oil and method for producing lubricating-oil base oil

ABSTRACT

There is provided a method for dewaxing a hydrocarbon oil for improving the life of a hydroisomerization catalyst. An aspect of a method for dewaxing a hydrocarbon oil according to the present invention comprises: a first step of subjecting a hydrocarbon oil in which a peroxide value is 100 ppm by mass or more to hydrotreating to obtain a material to be treated in which a peroxide value is 30 ppm by mass or less; and a second step of subjecting the material to be treated in which a peroxide value is 30 ppm by mass or less to hydroisomerization treatment using a hydroisomerization catalyst.

TECHNICAL FIELD

The present invention relates to a method for dewaxing a hydrocarbon oiland a method for producing a lubricant base oil.

BACKGROUND ART

Among petroleum products, for example, lubricant oils, gas oils, and jetfuels or the like are products in which cold flow property is regardedas important. When base oils used for these products contain waxycomponents such as normal paraffins or slightly branched isoparaffins,the cold flow property of the base oils decreases. Therefore, it isdesirable to completely or partially remove the waxy components in theproduction of the base oils. Alternatively, it is desirable that thewaxy components are completely or partially converted to componentsother than the waxy components. Hydrocarbons (hereinafter, referred toas “FT synthetic oils”) obtained by a Fischer-Tropsch reaction(hereinafter, referred to as a “FT reaction”) have recently attractedattention as feedstocks for producing lubricant oils or fuels, becausethey do not contain environmental load substances such as sulfurcompounds. However, because the FT synthetic oils also contain many waxycomponents, the waxy components in the FT synthetic oils are desirablyreduced.

As a dewaxing technique for removing waxy components from hydrocarbonoils, a method for extracting waxy components using a solvent such asliquefied propane or MEK (Methyl Ethyl Ketone) is known. However, thismethod has problems in that the operating costs of an extractingapparatus are high; the types of applicable feedstocks are limited; andthe product yield is limited by the type of feedstock.

On the other hand, as a dewaxing technique for converting waxycomponents in a hydrocarbon oil to non-waxy components, for example,catalytic dewaxing is known, in which the hydrocarbon oil is contacted,in the presence of hydrogen, with a so-called bifunctional catalysthaving hydrogenation-dehydrogenation function and isomerizationfunction, thereby isomerizing normal paraffins in the hydrocarbon oil toisoparaffins. As bifunctional catalysts used for catalytic dewaxing,solid acids are known. Among the solid acids, catalysts containingmolecular sieves made of zeolites, and metals belonging to Groups 8 to10 or Group 6 of the periodic table are known, and in particular,catalysts in which the metals are supported on molecular sieves areknown.

Catalytic dewaxing is an effective method for improving the cold flowproperty of hydrocarbon oils. It is necessary to sufficiently increasethe conversion rate of the normal paraffins in the hydrocarbon oils inorder to obtain a fraction that is suitable as a lubricant base oil or afuel base oil according to the catalytic dewaxing of the hydrocarbonoils. However, the above-mentioned catalysts used in catalytic dewaxinghave both isomerization function and hydrocarbon-cracking function.Therefore, in the catalytic dewaxing of the hydrocarbon oils, conversionof the hydrocarbon oil to lighter products also proceeds as theconversion rate of the normal paraffins increases, to make it difficultto obtain a desired fraction in high yield. Particularly when producinga high-quality lubricant base oil in which a high viscosity index and alow pour point are required, it is very difficult to economically obtainan intended fraction by the catalytic dewaxing of the hydrocarbon oil.For this reason, synthetic base oils such as poly-α-olefins have beenfrequently used in this field.

In recent years, however, in the fields of lubricant base oils and fuelbase oils or the like, the production of Group II, Group III, and GroupIII+ base oils using hydrotreating has become increasingly popular.Under such circumstances, there is a need for a hydroisomerizationcatalyst having both suppressed cracking activity for hydrocarbons andhigh isomerization reaction activity, i.e., having excellentisomerization selectivity, for the purpose of obtaining a desiredisoparaffin fraction in high yield from a hydrocarbon oil containingwaxy components.

Attempts to improve the isomerization selectivity of catalysts used incatalytic dewaxing have been made in the past. For example, thefollowing Patent Literature 1 discloses a hydroisomerization catalystincluding a molecular sieve (ZSM-22, ZSM-23, and ZSM-48 or the like)containing a metal of Group VIII or the like of the periodic table,having one-dimensional pores of an intermediate size, and having acrystallite size of not more than about 0.5 μm. The following PatentLiterature 1 discloses a process for producing a dewaxed lubricant oil,wherein a straight-chain or slightly branched hydrocarbon raw materialhaving 10 or more carbon atoms is contacted under isomerizationconditions with the above-mentioned hydroisomerization catalyst.

Zeolite that constitutes a hydroisomerization catalyst is typicallyproduced by hydrothermal synthesis in the presence of an organictemplate in order to construct a predetermined porous structure. Herein,the organic template is an organic compound having an amino group andammonium group or the like. The synthesized zeolite is calcined in anatmosphere containing molecular oxygen at a temperature of, for example,about 550° C. or more, thereby removing the organic template containedin the zeolite (see the final paragraph of “2.1. Materials” on page 453of the following Non-Patent Literature 1). The calcined zeolite ision-exchanged into an ammonium form in an aqueous solution containingammonium ions, for example (see “2.3. Catalytic experiments” on page 453of the following Non-Patent Literature 1). Metal components of Group 8to 10 or the like of the periodic table are further supported on theion-exchanged zeolite. The zeolite on which the metal component issupported is subjected to steps such as drying and optionally extruding,and then loaded in a reactor; the zeolite is calcined in an atmospherecontaining molecular oxygen at a temperature of about 400° C. Thecalcined zeolite is further subjected to reduction treatment with, forexample, hydrogen, at about the same temperature, and thereby thezeolite is provided with catalytic activity as a bifunctional catalyst.

Recently, there has been proposed a method for ion-exchanging zeolitesubjected to hydrothermal synthesis in a state where the zeolitecontains an organic template without calcining the zeolite at theabove-mentioned high temperature, to produce a hydroisomerizationcatalyst from the ion-exchanged zeolite, for the purpose of furtherimproving isomerization selectivity of the hydroisomerization catalyst(see the following Patent Literature 2).

CITATION LIST Patent Literature

-   Patent Literature 1: U.S. Pat. No. 5,282,958-   Patent Literature 2: Japanese Patent Application Laid-Open No.    2010-155187

Non Patent Literature

Non-Patent Literature 1: J. A. Martens et al., J. Catal. 239 (2006) 451

SUMMARY OF INVENTION Technical Problem

In the above-mentioned hydroisomerization catalyst, the reduced metalfunctions as an active site. Therefore, when a hydrocarbon oilcontaining strong oxidizer is contacted with the hydroisomerizationcatalyst, the metal that is the active site is oxidized to losecatalytic activity, which is apt to extremely shorten the life of thehydroisomerization catalyst. The short life of the catalyst poses aneconomical problem because it causes the catalyst costs to increase.

The present invention has been made in view of the above-mentionedproblems of the conventional technique, and an object of the presentinvention is to provide a method for dewaxing a hydrocarbon oil and amethod for producing a lubricant base oil for improving the life of ahydroisomerization catalyst.

Solution to Problem

An aspect of a method for dewaxing a hydrocarbon oil of the presentinvention comprises: a first step of subjecting a hydrocarbon oil inwhich a peroxide value is 100 ppm by mass or more to hydrotreating toobtain a material to be treated in which a peroxide value is 30 ppm bymass or less; and a second step of subjecting the material to be treatedin which a peroxide value is 30 ppm by mass or less tohydroisomerization treatment using a hydroisomerization catalyst.

In an aspect of the present invention, the hydrocarbon oil is preferablysynthesized by a Fischer-Tropsch reaction.

In an aspect of the present invention, it is preferable that thehydroisomerization catalyst contains zeolite; and the zeolite containsan organic template, and has a one-dimensional porous structureincluding a 10-membered ring.

In an aspect of the present invention, the zeolite is preferably atleast one selected from the group consisting of zeolite ZSM-22, zeoliteZSM-23, zeolite SSZ-32, and zeolite ZSM-48.

In an aspect of the present invention, it is preferable that thematerial to be treated contains normal paraffins those carbon numbersare 10 or more; and the material to be treated is contacted with thehydroisomerization catalyst in the presence of hydrogen in the secondstep.

An aspect of a method for producing a lubricant base oil of the presentinvention uses the above-mentioned method for dewaxing a hydrocarbonoil.

In an aspect of the method for producing a lubricant base oil of thepresent invention, it is preferable that the method further comprisesthe step of subjecting the material to be treated after thehydroisomerization treatment to hydrofinishing.

In an aspect of the method for producing a lubricant base oil of thepresent invention, it is preferable that the method further comprisesthe step of subjecting the material to be treated after thehydrofinishing to vacuum distillation.

Advantageous Effects of Invention

The present invention provides a method for dewaxing a hydrocarbon oiland a method for producing a lubricant base oil for improving the lifeof a hydroisomerization catalyst.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed. However, the present invention is not limited to thefollowing embodiments in any way.

[Method for Dewaxing Hydrocarbon Oil]

A method for dewaxing a hydrocarbon oil according to this embodimentcomprises a first step and a second step. The first step subjects ahydrocarbon oil in which a peroxide value is 100 ppm by mass or more tohydrotreating to obtain a material to be treated in which a peroxidevalue is 30 ppm by mass or less. The second step (dewaxing step)subjects the material to be treated in which a peroxide value is reducedto 30 ppm by mass or less in the first step to hydroisomerizationtreatment using a hydroisomerization catalyst.

(Hydrocarbon Oil)

A hydrocarbon oil derived from petroleum may be used as a hydrocarbonoil that is a raw material, and an FT synthetic oil synthesized by aFischer-Tropsch reaction may be used. In this embodiment, thehydrocarbon oil is preferably the FT synthetic oil (particularly, an FTwax). The sulfur content and aromatic hydrocarbon in the FT syntheticoil are lower than that of the hydrocarbon oil derived from thepetroleum. Therefore, a lubricant base oil and a fuel base oil or thelike in which a load on the environment is reduced can be produced byusing the FT synthetic oil as a raw material. Because the sulfur contentis a catalyst poison of a catalyst for hydrotreating orhydroisomerization catalyst, the poisoning of the catalyst is suppressedby using an FT synthetic oil in which the sulfur content is low, toeasily improve the life of the catalyst. Hereinafter, a case where thehydrocarbon oil is the FT synthetic oil will be described.

The FT synthetic oil is produced, for example, by the following method.First, natural gas as a raw material is desulfurized. Specifically, asulfur compound in the natural gas is converted to hydrogen sulfide by ahydrodesulfurization catalyst, or is removed by using a materialadsorbing the hydrogen sulfide.

High-temperature synthesis gas primarily containing carbon monoxide gasand hydrogen gas is generated according to the reforming reaction(reforming) of the desulfurized natural gas. The reforming reaction ofthe natural gas is represented by the following chemical reactionequations (1) and (2). A reforming method is not limited to a watervapor-carbon dioxide reforming method using carbon dioxide and watervapor. For example, a water vapor reforming method, a partial oxidationreforming method (PDX) using oxygen, an autothermal reforming method(ATR) that is a combination of the partial oxidation reforming methodand the water vapor reforming method, and a carbon dioxide reformingmethod or the like can also be utilized.

CH₄+H₂O→CO+3H₂  (1)

CH₄+CO₂→2CO+2H₂  (2)

The hydrogen gas and the carbon monoxide gas in the synthesis gas arereacted with each other. That is, the FT synthetic oil is generated bymaking an FT reaction exemplified by the following chemical reactionequation (3) proceed.

(2n+1)H₂ +nCO→CnH_(2n+2) +nH₂O  (3)

A catalyst in which an active metal is supported on an inorganic supportis used as a catalyst for the FT reaction (FT catalyst). Examples of theinorganic support include porous oxides such as silica, alumina,titania, magnesia, and zirconia. Examples of the active metal includecobalt, ruthenium, iron, and nickel. A compound containing metalelements such as zirconium, titanium, hafnium, sodium, lithium, andmagnesium in addition to the above-mentioned active metal may besupported on the FT catalyst. These components improve catalyticactivity or contribute to control of the number of carbon atoms of theFT synthetic oil and distribution thereof.

The FT synthetic oil is a mixture of straight-chain hydrocarbons (normalparaffins) in which the number of carbon atoms is about 1 to 100, andhardly contains aromatic hydrocarbons, naphthenic hydrocarbons, andisoparaffins. An FT wax in which the number of carbon atoms is about 21or more, and a boiling point is more than about 360° C. is contained inthe FT synthetic oil.

(Summary of First Step and Second Step)

In this embodiment, the FT wax in the FT synthetic oil is dewaxed. Amethod for producing the lubricant base oil, the fuel base oil, or thelike utilizing the FT reaction is roughly divided into a so-called GTL(Gas To Liquids) step as described above and a dewaxing-distilling stepof the FT synthetic oil (FT wax). Conventionally, a plant (GTL plant)for carrying out the GTL step and a plant (dewaxing plant) for carryingout the dewaxing-distilling step of the FT wax are not necessarilyadjacent to each other. For example, the GTL plant is often located in aforeign country where an extracting gas well exists, and the dewaxingplant is often located in the country (Japan). Thus, when the GTL plantand the dewaxing plant are far apart from each other, it is necessary totransport the FT wax produced in the GTL plant to the dewaxing plant.Because the transportation requires a long time of about several months,the FT wax is oxidized by oxygen in the atmosphere during thetransportation. If the synthesized FT wax is stored for a long period oftime even when the GTL plant and the dewaxing plant are not far apartfrom each other, the FT wax is oxidized.

The present inventors discovered that the FT wax oxidized during thetransportation oxidizes a metal that is the active site of thehydroisomerization catalyst used for the dewaxing step after thetransportation, and thereby the activity of the hydroisomerizationcatalyst is reduced. That is, the present inventors found that theoxidizer of the FT wax after the transportation is one of factors thatshorten the life of the hydroisomerization catalyst. An object of thefirst step in this embodiment is to improve the life of thehydroisomerization catalyst used for the dewaxing step (second step) asdescribed below.

In the first step of this embodiment, the FT wax oxidized during thetransportation is subjected to hydrotreating to weaken the oxidizer ofthe FT wax. Herein, although the hydrotreating in the first step meansreduction due to hydrogenation, at least any of the hydrocracking,hydroisomerization, or hydrorefining (desulfurization anddenitrification or the like) of the FT wax may proceed by thehydrotreating. In the second step (dewaxing step), the FT wax issubjected to hydroisomerization treatment before the FT wax is oxidizedagain. That is, after the FT wax is transported to the dewaxing plantfrom the GTL plant in this embodiment, the FT wax oxidized during thetransportation is subjected to hydrotreating in the dewaxing plant.Before the FT wax reduced by the hydrotreating is oxidized again, thedewaxing of the FT wax is carried out. As a result, thehydroisomerization catalyst for dewaxing is hardly oxidized by the FTwax, to improve the life of the catalyst. That is, because the FT wax issubjected to the hydrotreating just before the dewaxing step (after thetransportation or after storage) in this embodiment, the life of thehydroisomerization catalyst can be improved irrespective of the lengthof a transportation time or a storage time.

Other examples of the method for reducing the oxidation nature of the FTwax include hydrotreating to the FT wax before transportation orstorage, or addition of an antioxidant to the FT wax. However, it isdifficult to sufficiently suppress the oxidization of the FT wax that isassociated with the transportation or the storage according to onlythese methods. On the other hand, because the FT wax is reduced by thehydrotreating just before the dewaxing step in this embodiment, the lifeof the hydroisomerization catalyst can be certainly improved withoutusing other methods.

The above-mentioned first step and second step are quantitativelyexpressed as follows. That is, in the first step, the hydrocarbon oil inwhich the peroxide value is 100 ppm by mass or more is subjected to thehydrotreating to reduce the peroxide value to 30 ppm by mass or less. Inthe second step (dewaxing step), the material to be treated in which theperoxide value is maintained at 30 ppm by mass or less is subjected tothe hydroisomerization treatment.

Herein, the peroxide value is a ratio (unit:ppm by mass or mg/kg) of themass of hydroperoxide (peroxide) contained in the hydrocarbon oil (FTwax) to the total mass of the hydrocarbon oil. When the hydrocarbon oiltakes in oxygen in the air, the hydrocarbon oil is oxidized, to generatethe hydroperoxide, which increases the peroxide value. The larger theperoxide value of the hydrocarbon oil is, the higher the oxidationnature of the hydrocarbon oil is. Therefore, the hydrocarbon oil (FTwax) in which the peroxide value is 100 ppm by mass or more means ahydrocarbon oil (FT wax) having oxidation nature that is high enough todegrade the hydroisomerization catalyst.

Although a method for measuring the peroxide value in this embodiment isbased on the Japan Petroleum Institute method JPI-5S-46-96 “TestingMethod for Peroxide Number of Kerosine”, the method is a method in whichkerosene is replaced by a hydrocarbon oil in the test method. In thisembodiment, the peroxide value is measured by making hydroperoxide in ahydrocarbon oil react with potassium iodide, and titrating free iodinewith a sodium thiosulfate solution. The specific procedure of themeasurement is as follows. First, a sample (hydrocarbon oil) isprecisely measured off. A liquid mixture of chloroform and glacialacetic acid (volume ratio 2:3) was added into the sample put into astoppered Erlenmeyer flask, to dissolve the sample. When the sample isnot uniformly dissolved, the liquid mixture of chloroform and glacialacetic acid is further suitably added. Subsequently, while air in theflask is replaced by nitrogen gas or carbon dioxide, a saturatedpotassium iodide solution is added into the liquid mixture in which thesample is dissolved, and a stopper is immediately closed. After theliquid mixture in the flask is mixed for several minutes, a starch testsolution as an indicator was added into the liquid mixture, and iodinein the liquid mixture was titrated with a sodium thiosulfate solution.

If the second step (dewaxing step) is carried out for the FT wax inwhich the peroxide value is 100 ppm by mass or more without the firststep, the noble metal that is the active site of the hydroisomerizationcatalyst is oxidized by the FT wax, to shorten the life of the catalyst.However, in this embodiment, the FT wax is reduced by the hydrotreatingin the first step. As a result, a material to be treated in which aperoxide value is reduced to 30 ppm by mass or less and oxidation natureis low is obtained. Therefore, in the second step, the oxidization ofthe hydroisomerization catalyst by the material to be treated hardlyoccurs to improve the life of the catalyst. The refining(desulfurization or the like) of the hydrocarbon oil also proceeds bythe hydrotreating in the first step to obtain the material to be treatedin which the content of the catalyst poison (sulfur or the like) isreduced. Therefore, in the second step, the poisoning of thehydroisomerization catalyst by the catalyst poison in the material to betreated also hardly occurs to improve the life of the catalyst.

If the hydroisomerization is carried out after the material to betreated obtained in the first step is oxidized again and the peroxidevalue is more than 30 ppm by mass, the hydroisomerization catalyst isoxidized by the material to be treated, which makes it difficult toimprove the life of the catalyst. However, in this embodiment, thehydroisomerization is carried out before the peroxide value of thematerial to be treated is more than 30 ppm by mass by the oxidizationafter the first step, which makes it possible to improve the life of thehydroisomerization catalyst.

The upper limit value of the peroxide value of the hydrocarbon oil (FTwax) just before the first step is about 2000 ppm by mass, for example.If the first step is carried out for the hydrocarbon oil in which theperoxide value is 2000 ppm by mass or less, the peroxide value of thematerial to be treated obtained in the first step is easily reduced to30 ppm by mass or less, and an effect of improving the life of thehydroisomerization catalyst used in the second step is easily obtained.If the first step is carried out for the hydrocarbon oil in which theperoxide value is 2000 ppm by mass or less, the oxidization anddegradation of the catalyst for hydrotreating used in the first step aresuppressed, and the life of the catalyst for hydrotreating is alsoimproved. In this embodiment, the range of the peroxide value of thehydrocarbon oil (FT wax) just before the first step may be 100 to 2000ppm by mass, 100 to 500 ppm by mass, or about 130 to 450 ppm by mass.

The peroxide value of the material to be treated obtained in the firststep is 0 to 30 ppm by mass, and preferably 0 to 1 ppm by mass. That is,in the first step, the peroxide value of the hydrocarbon oil (FT wax) isreduced to 0 to 30 ppm by mass, and preferably 0 to 1 ppm by mass. Inother words, until the hydroisomerization treatment is started, theperoxide value of the material to be treated is maintained at 0 to 30ppm by mass, and preferably at 0 to 1 ppm by mass. When the peroxidevalue of the material to be treated is lower, the oxidization anddegradation of a catalyst for hydroisomerization treatment aresuppressed, and the life of the catalyst for hydroisomerizationtreatment is easily improved. In order to suppress the reoxidization ofthe material to be treated and to maintain the peroxide value at 30 ppmby mass or less, the material to be treated may be held in an inactiveatmosphere or an nonoxidative atmosphere (for example, a storage tank ora transfer pipe shut off from the atmosphere), for example, until thesecond step is performed. If a time after the first step before thesecond step is shortened as much as possible, the reoxidization of thematerial to be treated can be suppressed.

(Specific Aspect of First Step)

In the hydrotreating in the first step, the hydrocarbon oil (FT wax) maybe contacted with the catalyst for hydrotreating. A method for producingthe catalyst for hydrotreating comprises a supporting step and acalcining step. The supporting step supports an active metal componentcontaining an active metal element on a support to obtain a catalystprecursor. The calcining step calcines the precursor obtained in thesupporting step to obtain the catalyst for hydrotreating. A support inwhich the content of a carbonaceous material containing a carbon atom is0.5% by mass or less in terms of the carbon atom may be used as thesupport. At least one selected from metals belonging to Groups 6, 8, 9,and 10 of the periodic table may be used as the active metal element.The periodic table means a long period type element periodic tableestablished by the International Union of Pure and Applied Chemistry(IUPAC).

The catalyst for hydrotreating may be a hydrocracking catalyst. Thecatalyst for hydrotreating may be a hydrorefining catalyst.

When the catalyst for hydrotreating is the hydrocracking catalyst, thesupport is preferably a support containing crystalline zeolites such asultrastable Y (USY)-type zeolite, Y-type zeolite, mordenite, and βzeolite, and one or more solid acids selected from amorphous compositemetal oxides such as silica-alumina, silica-zirconia, alumina-boria,alumina-zirconia, silica-titania, and silica-magnesia.

When the catalyst for hydrotreating is the hydrocracking catalyst, thesupport is preferably a support containing USY-type zeolite, and one ormore selected from silica-alumina, alumina-boria, and silica-zirconia.The support is more preferably a support containing USY-type zeolite,and one or more selected from alumina-boria and silica-alumina.

The USY-type zeolite is obtained by ultrastabilizing the Y-type zeoliteaccording to hydrothermal treatment and/or acid treatment. The USY-typezeolite includes a fine porous structure intrinsically included in theY-type zeolite. This fine porous structure is a structure includingmicropores having a pore diameter of 2 nm or less. In addition to theabove-mentioned fine porous structure, new pores in which a porediameter is 2 to 10 nm are further formed in the USY-type zeolite.Although the mean particle size of the USY-type zeolite is notparticularly limited, the mean particle size is preferably 1.0 μm orless, and more preferably 0.5 μm or less. The molar ratio (the molarratio of silica to alumina) of silica/alumina in the USY-type zeolite ispreferably 10 to 200, more preferably 15 to 100, and still morepreferably 20 to 60.

The support of the hydrocracking catalyst preferably contains 0.1 of 80%by mass of crystalline zeolite and 0.1 to 60% by mass of an amorphouscomposite metal oxide.

A binder may be mixed in the support of the hydrocracking catalyst forthe purpose of improving the extrudability and mechanical strength ofthe support. Preferred examples of the binder include alumina, silica,and magnesia. Although the mixing amount of the binder is notparticularly limited, the mixing amount is preferably 20 to 98% by massbased on the total mass of the support, and more preferably 30 to 96% bymass.

The support of the hydrocracking catalyst is preferably extruded.Although the shape of the extruded support is not particularly limited,examples of the shape include a spherical shape, a cylindrical shape, anirregular tubular shape having a three leaf-shaped or four leaf-shapedcross section, and a disc shape. A method for forming the support is notlimited, and known methods such as extrusion and tablet molding areused. The extruded support is typically calcined.

The active metal element contained in the hydrocracking catalyst ispreferably at least one selected from the group consisting of metalsbelonging to Groups 8 to 10 of the periodic table. Suitable examples ofthe active metal element include cobalt, nickel, rhodium, palladium,iridium, and platinum. Among these metals, at least one selected fromnickel, palladium, and platinum is more preferably used, and at leastone selected from palladium and platinum is still more preferably used.

When the active metal element contained in the hydrocracking catalyst isa metal other than noble metals such as cobalt and nickel, the contentof the active metal element is preferably 2 to 50 parts by mass in termsof a metal oxide based on the total mass of the support. When the activemetal element supported on the support in the hydrocracking catalyst isa noble metal such as platinum, palladium, rhodium, or indium, thecontent of the active metal element is preferably 0.1 to 3.0 parts bymass in terms of a metal atom based on the total mass of the support.When the content of the active metal element is less than theabove-mentioned lower limit value, the hydrocracking tends not tosufficiently proceed. On the other hand, when the content of the activemetal element is more than the above-mentioned upper limit value, thedispersion of the active metal element tends to decrease to decrease theactivity of the catalyst, and the catalyst costs increase.

When the catalyst for hydrotreating of this embodiment is thehydrorefining catalyst, the support is preferably a support containingmetal oxides such as alumina, silica, titania, zirconia, and boria. Thesupport of the hydrorefining catalyst may be a support containingcomposite metal oxides such as silica-alumina, silica-zirconia,alumina-boria, alumina-zirconia, silica-titania, and silica-magnesia.

The support of the hydrorefining catalyst preferably contains acomposite metal oxide having solid acidity such as silica-alumina,silica-zirconia, alumina-zirconia, and alumina-boria. Thereby, it ispossible to allow the hydroisomerization of a linear aliphatichydrocarbon to efficiently proceed simultaneously with thehydrorefining. The support may contain a small amount of zeolite.

A binder may be mixed in the support of the hydrorefining catalyst forthe purpose of improving the extrudability and mechanical strength ofthe support. Preferred examples of the binder include alumina, silica,and magnesia. Although the mixing amount of the binder is notparticularly limited, the mixing amount is preferably 20 to 98 parts bymass based on the total mass of the support, and more preferably 30 to96 parts by mass.

The support of the hydrorefining catalyst is preferably extruded.Although the shape of the extruded support is not particularly limited,examples of the shape include a spherical shape, a cylindrical shape, anirregular tubular shape having a three leaf-shaped or four leaf-shapedcross section, and a disc shape. A method for forming the support is notlimited, and known methods such as extrusion and tablet molding areused. The extruded support is typically calcined.

The active metal element contained in the hydrorefining catalyst ispreferably at least one selected from the group consisting of metalsbelonging to Groups 6, 8, 9, and 10 of the periodic table. Suitableexamples of the active metal element include noble metals such asplatinum, palladium, rhodium, ruthenium, iridium, and osmium, or cobalt,nickel, molybdenum, tungsten, and iron. The active metal element ispreferably platinum, palladium, nickel, cobalt, molybdenum, or tungsten,and more preferably platinum or palladium. A plurality of these metalsmay be used in combination. Preferred examples of the combination of theactive metal elements include platinum-palladium, cobalt-molybdenum,nickel-molybdenum, nickel-cobalt-molybdenum, and nickel-tungsten.

When the active metal element supported on the support in thehydrorefining catalyst is the noble metal, the content of the activemetal element is preferably 0.1 to 3.0 parts by mass in terms of a metalatom based on the total mass of the support. When the active metalelement supported on the support in the hydrorefining catalyst is ametal other than the noble metal, the content of the active metalelement is preferably 2 to 50 parts by mass in terms of a metal oxidebased on the total mass of the support. When the content of the activemetal element is less than the above-mentioned lower limit value, thehydrorefining and the hydroisomerization tend not to sufficientlyproceed. When the content of the active metal element is more than theabove-mentioned upper limit value, the dispersibility of the activemetal element tends to decrease to decrease the activity of thecatalyst, and the catalyst costs increase.

In a hydrotreating apparatus for carrying out the hydrotreating in thefirst step, a crude wax fraction and an uncracked wax fraction (ahydrocarbon of about C₂₁ or more) that constitute the FT wax arepartially converted to a hydrocarbon in which the number of carbon atomsis about C₂₀ or less by the hydrocracking. Furthermore, the hydrocarbonis partially converted to a naphtha fraction (about C₅ to C₁₀) lighterthan a middle fraction (about C₁₁ to C₂₀) by excessive cracking, and isfurther converted to a gaseous hydrocarbon of C₄ or less. On the otherhand, partially, the crude wax fraction and the uncracked wax fractiondo not sufficiently undergo the hydrocracking, and become the uncrackedwax fraction of about C₂₁ or more. The composition of a hydrocrackedproduct is determined by the hydrocracking catalyst to be used andhydrocracking reaction conditions. Herein, the “hydrocracked product”refers to all hydrocracked products containing the uncracked waxfraction unless otherwise specified. If the hydrocracking reactionconditions are made severe beyond necessity, the content of theuncracked wax fraction in the hydrocracked product decreases, however, alight component in which a molecular weight is equal to or less thanthat of the naphtha fraction increases, to decrease the yield of themiddle fraction. On the other hand, if the hydrocracking reactionconditions are eased beyond necessity, the uncracked wax fractionincreases, to decrease the yield of the middle fraction. When the massof all the cracked products in which a boiling point is 25° C. or moreis M1 and the mass of the cracked product in which a boiling point is 25to 360° C. is M2, a cracking rate M2/M1 is about 10 to 90%. The crackingrate M2/M1 is preferably 20 to 80%, and more preferably 25 to 50%. Thecracking rate M2/M1 is adjusted by suitably setting each reactioncondition of the hydrotreating.

In the hydrotreating apparatus, in parallel to a hydrocracking reaction,the hydroisomerization reaction of the normal paraffins constituting thecrude wax fraction and the uncracked wax fraction, or the hydrocrackedproducts thereof proceeds, to generate the isoparaffins. When thehydrocracked product is used as a fuel oil base, the isoparaffinsgenerated according to the hydroisomerization reaction are componentscontributing to improvement in the cold flow property, and thegeneration rate is preferably high. Furthermore, the removal ofoxygen-containing compounds such as olefins and alcohols that arecontained in the crude wax fraction and are by-products of an FTsynthesis reaction also proceeds. That is, the olefins are converted toa paraffin hydrocarbon by the hydrogenation, and the oxygen-containingcompounds are converted to the paraffin hydrocarbon and water byhydrogenation deoxygenation.

In the first step, the hydrotreating may be carried out under each ofthe following step conditions in order to reduce the peroxide value ofthe FT wax to a value of 30 ppm by mass or less from a value of 100 ppmby mass or more.

The reaction temperature of the hydrotreating is about 180 to 400° C.,preferably 200 to 370° C., more preferably 250 to 350° C., andparticularly preferably 280 to 350° C. Although the peroxide value isreduced when the reaction temperature is more than 400° C., the crackingof the FT wax to the light component proceeds, which tends to decreasethe yields of the middle fraction and heavy component and to color theproduct, thereby limiting the use of the product as the fuel oil base.On the other hand, when the reaction temperature is less than 180° C.,the peroxide value cannot be reduced. Furthermore, the hydrocrackingreaction does not sufficiently proceed, to decrease the yield of themiddle fraction and to suppress the generation of the isoparaffinsaccording to the hydroisomerization reaction, and the oxygen-containingcompounds such as alcohols tend to remain without being sufficientlyremoved.

A hydrogen partial pressure in a hydrotreating reaction is about 0.5 to12 MPa, and preferably 1.0 to 5.0 MPa. When the hydrogen partialpressure is less than 0.5 MPa, the hydrocracking and thehydroisomerization or the like tend not to sufficiently proceed. On theother hand, when the hydrogen partial pressure is more than 12 MPa, highpressure resistance is required for the hydrotreating apparatus, andfacility costs tend to increase.

The liquid hourly space velocity (LHSV) of the FT wax (the crude waxfraction and the uncracked wax fraction) in the hydrotreating reactionis about 0.1 to 10.0 h⁻¹, and preferably 0.3 to 3.5 hr⁻¹. When the LHSVis less than 0.1 hr⁻¹, excessive hydrocracking tends to proceed,resulting in lowered productivity. Conversely, when the LHSV is morethan 10.0 hr⁻¹, the peroxide value cannot be reduced, and thehydrocracking and the hydroisomerization or the like tend not tosufficiently proceed.

A hydrogen/oil ratio (a hydrogen/FT wax ratio) is about 50 to 1000Nm³/m³, and preferably 70 to 800 Nm³/m³. When the hydrogen/oil ratio isless than 50 Nm³/m³, the hydrocracking and the hydroisomerization or thelike tend not to sufficiently proceed. Conversely, when the hydrogen/oilratio is more than 1000 Nm³/m³, a large-scale hydrogen feed apparatus orthe like tends to be required.

The amount of the catalyst for hydrotreating used and the time requiredfor the hydrotreating, or the like may be suitably adjusted according tothe amount of the FT wax, the peroxide value of the FT wax before thehydrotreating, and each of the above-mentioned reaction conditions, orthe like.

(Specific Aspect of Second Step)

The hydroisomerization catalyst used in the second step is producedaccording to a specific method, and is thereby provided with itsfeatures. Hereinafter, the hydroisomerization catalyst will be describedaccording to its preferred production aspect. This embodiment cansignificantly improve the life of the following hydroisomerizationcatalyst particularly.

A method for producing the hydroisomerization catalyst of thisembodiment comprises a first step of heating a mixture containing anion-exchanged zeolite obtained by ion-exchanging an organictemplate-containing zeolite containing an organic template and having a10-membered ring one-dimensional porous structure in a solutioncontaining ammonium ions and/or protons, and a binder at a temperatureof 250 to 350° C. in a N₂ atmosphere to obtain a support precursor, anda second step of calcining a catalyst precursor in which a platinum saltand/or a palladium salt are/is contained in the support precursor at atemperature of 350 to 400° C. in an atmosphere containing molecularoxygen to obtain a hydroisomerization catalyst in which platinum and/orpalladium are/is supported on the support containing the zeolite.

The organic template-containing zeolite used in this embodiment has aone-dimensional porous structure including a 10-membered ring, in viewof achieving a high level of both high isomerization activity andsuppressed cracking activity in the hydroisomerization reactions ofnormal paraffins. Examples of such zeolites include AEL, EUO, FER, HEU,MEL, MFI, NES, TON, MTT, WEI, *MRE, and SSZ-32. The above-mentionedthree alphabet letters mean framework type codes assigned to structuresof classified molecular sieve-type zeolites by the Structure Commissionof the International Zeolite Association. Zeolites having the sametopology are collectively designated by the same code.

Among the above-mentioned zeolites having one-dimensional porousstructures including a 10-membered ring, the organic template-containingzeolite are preferably zeolites having a TON and MIT structures, zeoliteZSM-48 that is zeolite having an *MRE structure, and zeolite SSZ-32 inview of high isomerization activity and low cracking activity. ZeoliteZSM-22 is more preferred among zeolites having the TON structure, andzeolite ZSM-23 is more preferred among zeolites having the MTTstructure.

The organic template-containing zeolite is hydrothermally synthesizedaccording to a known method using a silica source, an alumina source,and an organic template that is added to construct the predeterminedporous structure described above.

The organic template is an organic compound having an amino group and anammonium group or the like, and is selected according to the structureof the zeolite to be synthesized, however, the organic template ispreferably an amine derivative. Specifically, the organic template ispreferably at least one selected from the group consisting ofalkylamine, alkyldiamine, alkyltriamine, alkyltetramine, pyrrolidine,piperazine, aminopiperazine, alkylpentamine, alkylhexamine, and theirderivatives. The carbon number of above alkyl group may be 4 to 10,preferably 6 to 8. Typical examples of the alkyldiamines include1,6-hexanediamine and 1,8-diaminooctane.

The molar ratio of the silicon element to the aluminum element([Si]/[Al], hereinafter referred to as the “Si/Al ratio”) both of whichconstitute the organic template-containing zeolite having a 10-memberedring one-dimensional porous structure is preferably 10 to 400, and morepreferably 20 to 350. When the Si/Al ratio is less than 10, although theactivity for the conversion of the normal paraffins increases, theisomerization selectivity to isoparaffins tends to decrease, andcracking reactions tend to sharply increase as the reaction temperatureincreases, which is undesirable. Conversely, if the Si/Al ratio is morethan 400, catalytic activity needed for the conversion of the normalparaffins cannot be easily obtained, which is undesirable.

The synthesized organic template-containing zeolite that has preferablybeen washed and dried typically has alkali metal cations as countercations, and incorporates the organic template in its porous structure.The zeolite containing an organic template, which is used for producingthe hydroisomerization catalyst of the present invention is preferablyin such a synthesized state, i.e., preferably, the zeolite has not beensubjected to calcination treatment for removing the organic templateincorporated therein.

The organic template-containing zeolite is subsequently ion-exchanged ina solution containing ammonium ions and/or protons. By the ion-exchangetreatment, the counter cations contained in the organictemplate-containing zeolite are exchanged into ammonium ions and/orprotons. At the same time, a portion of the organic templateincorporated in the organic template-containing zeolite is removed.

The solution used for the ion-exchange treatment is preferably asolution that uses a solvent containing at least 50% by volume of water,and more preferably an aqueous solution. Examples of compounds forsupplying ammonium ions into the solution include various inorganic andorganic ammonium salts such as ammonium chloride, ammonium sulfate,ammonium nitrate, ammonium phosphate, and ammonium acetate. On the otherhand, mineral acids such as hydrochloric acid, sulfuric acid, and nitricacid are typically utilized as compounds for supplying protons into thesolution. The ion-exchanged zeolite (herein, an ammonium-form zeolite)obtained by ion exchange of the organic template-containing zeolite inthe presence of ammonium ions releases ammonia during subsequentcalcination, and the counter cations are converted to protons to formBronsted acid sites. Ammonium ions are preferred as the cationic speciesused for the ion exchange. The content of ammonium ions and/or protonscontained in the solution is preferably set to 10 to 1000 equivalentsrelative to the total amount of the counter cations and organic templatecontained in the organic template-containing zeolite used.

The ion-exchange treatment may be applied to the organictemplate-containing zeolite support in powder form; alternatively, priorto the ion-exchange treatment, the organic template-containing zeolitemay be mixed with an inorganic oxide that is a binder, and extruded, andthe ion-exchange treatment may be applied to the resulting extrudedbody. However, if the above-mentioned extruded body is subjected to theion exchange treatment without being calcined, the problems ofcollapsing and powdering of the extruded body will easily arise;therefore, it is preferred to subject the organic template-containingzeolite in powder form to the ion-exchange treatment.

The ion-exchange treatment is preferably performed according to astandard method, i.e., a method in which the zeolite containing anorganic template is immersed in a solution containing ammonium ionsand/or protons, preferably, an aqueous solution, and the solution isstirred or fluidized. The stirring or fluidization is preferablyperformed under heating to improve the ion-exchange efficiency. In thepresent invention, a method in which the aqueous solution is heated,boiled, and ion-exchanged under reflux is particularly preferred.

Further, in view of improving the ion-exchange efficiency, during theion exchange of the zeolite in a solution, the solution is preferablyexchanged with a fresh one once or twice or more, and more preferablyexchanged with a fresh one once or twice. When the solution is exchangedonce, the ion-exchange efficiency can be improved by, for example,immersing the organic template-containing zeolite in a solutioncontaining ammonium ions and/or protons, and heating the solution underreflux for 1 to 6 hours, followed by exchanging the solution with afresh one, and further heating under reflux for 6 to 12 hours.

By the ion-exchange treatment, substantially all of the counter cationssuch as an alkali metal in the zeolite can be exchanged into ammoniumions and/or protons. On the other hand, with respect to the organictemplate incorporated in the zeolite, although a portion of the organictemplate is removed by the ion-exchange treatment, it is generallydifficult to remove the entire organic template even if the ion-exchangetreatment is repeatedly performed, resulting in a portion of the organictemplate remaining inside the zeolite.

In this embodiment, a mixture containing ion-exchanged zeolite and abinder is heated at a temperature of 250 to 350° C. in a nitrogenatmosphere to obtain a support precursor.

The mixture containing the ion-exchanged zeolite and the binder ispreferably a extruded body obtained by mixing an inorganic oxide intothe ion-exchanged zeolite obtained by the above-mentioned method that isa binder, and extruding the obtained composition. The purpose of mixingan inorganic oxide into the ion-exchanged zeolite is to increase themechanical strength of the support (in particular, a particulatesupport) obtained by calcining the extruded body to a degree that thesupport can withstand practical applications, however, the presentinventors have found that the selection of the type of inorganic oxideaffects the isomerization selectivity of the hydroisomerizationcatalyst. From this viewpoint, at least one inorganic oxide selectedfrom alumina, silica, titania, boria, zirconia, magnesia, ceria, zincoxide, phosphorus oxide, and a composite oxide containing a combinationof two or more of these oxides is used as the above-mentioned inorganicoxide. Among the above, silica and alumina are preferred in view offurther improving the isomerization selectivity of thehydroisomerization catalyst, and alumina is more preferred. The phrase“composite oxide containing a combination of two or more of theseoxides” is a composite oxide containing at least two components fromalumina, silica, titania, boria, zirconia, magnesia, ceria, zinc oxide,and phosphorus oxide, but is preferably an alumina-based composite oxidecontaining 50% by mass or more of an alumina component based on thecomposite oxide, and more preferably alumina-silica.

The proportion of the ion-exchanged zeolite to the inorganic oxidecontained in the above-mentioned composition is preferably 10:90 to90:10, and more preferably 30:70 to 85:15, in terms of the mass ratio ofthe ion-exchanged zeolite to the inorganic oxide. When this ratio isless than 10:90, the activity of the hydroisomerization catalyst tendsto be insufficient, which is undesirable. Conversely, when the ratio ismore than 90:10, the mechanical strength of the support obtained byextruding and calcining the composition tends to be insufficient, whichis undesirable.

Although the method for mixing the above-mentioned inorganic oxide intothe ion-exchanged zeolite is not particularly limited, a general methodcan be employed, such as a method in which a suitable amount of a liquidsuch as water is added to the powders of both components to form aviscous fluid, and the fluid is kneaded in a kneader or the like.

The composition containing the above-mentioned ion-exchanged zeolite andthe above-mentioned inorganic oxide, or a viscous fluid containing thecomposition is formed by extrusion or the like, and is preferably dried,to form a particulate extruded body. Although the shape of the extrudedbody is not particularly limited, examples of the shape include acylindrical shape, a pellet shape, a spherical shape, and an irregulartubular shape having a three leaf-shaped or four leaf-shaped crosssection. Although the size of the extruded body is not particularlylimited, the extruded body is preferably, for example, about 1 to 30 mmin long axis, and about 1 to 20 mm in short axis in view of the ease ofhandling, and the load density in the reactor or the like.

In this embodiment, the extruded body obtained as described above ispreferably heated at a temperature of 250 to 350° C. in a N₂ atmosphereto form the support precursor. A heating time is preferably 0.5 to 10hours, and more preferably 1 to 5 hours.

When the above-mentioned heating temperature is less than 250° C. inthis embodiment, the organic template remains in a large amount, andzeolite pores are plugged by the remaining template. Isomerizationactive sites are considered to exist near pore-mouth; a reactivesubstrate cannot be diffused into the pores by pore blockage in theabove-mentioned case; the active sites are covered, and thereby anisomerization reaction does not easily proceed, and the conversion rateof the normal paraffins tends to be hardly obtained sufficiently. On theother hand, when the heating temperature is more than 350° C., theisomerization selectivity of the obtained hydroisomerization catalyst isnot sufficiently improved.

A lower limit temperature when the extruded body is heated to form thesupport precursor is preferably 280° C. or more. An upper limittemperature is preferably 330° C. or less.

In this embodiment, the above-mentioned mixture is preferably heatedsuch that a potion of the organic template contained in theabove-mentioned extruded body remains. Specifically, heating conditionsare preferably set such that the amount of carbon in thehydroisomerization catalyst obtained by calcination after metalsupporting, which will be described below, is 0.4 to 3.5% by mass,preferably 0.4 to 3.0% by mass, more preferably 0.4 to 2.5% by mass, andthe micro-pore volume per unit mass of the catalyst is 0.02 to 0.12cc/g, which will be described below, and the micro-pore volume per unitmass of the zeolite contained in the catalyst is 0.01 to 0.12 cc/g.

Next, the catalyst precursor in which the platinum salt and/or thepalladium salt are/is contained in the above-mentioned support precursoris calcined at a temperature of 350 to 400° C., preferably 380 to 400°C., and more preferably 400° C. in an atmosphere containing molecularoxygen, to obtain a hydroisomerization catalyst in which platinum and/orpalladium are/is supported on the support containing zeolite. The phrase“in an atmosphere containing molecular oxygen” means contacting with gascontaining oxygen gas, and preferably air. A calcining time ispreferably 0.5 to 10 hours, and more preferably 1 to 5 hours.

Examples of the platinum salts include chloroplatinic acid,tetraamminedinitroplatinum, dinitroaminoplatinum, andtetraamminedichloroplatmum. Because the chloride salt generateshydrochloric acid during the reaction to possibly cause the corrosion ofthe apparatus, tetraamminedinitroplatinum that is a platinum salt inwhich platinum is highly dispersed other than the chloride salt ispreferred.

Examples of the palladium salts include palladium chloride, tetraamminepalladium nitrate, and diaminopalladium nitrate. Because the chloridesalt generates hydrochloric acid during the reaction to possibly causethe corrosion of the apparatus, tetraammine palladium nitrate that is apalladium salt in which palladium is highly dispersed other than thechloride salt is preferred.

The amount of the active metal supported on the support containing thezeolite of this embodiment is preferably 0.001 to 20% by mass based onthe mass of the support, and more preferably 0.01 to 5% by mass. Whenthe amount of the supported metal is less than 0.001% by mass, it willbe difficult to impart a predetermined hydrogenation/dehydrogenationfunction. Conversely, when the amount of the supported metal is morethan 20% by mass, the conversion of hydrocarbons to lighter products onthe active metal by cracking tends to easily proceed, to cause the yieldof an intended fraction to decrease, and further to cause the catalystcosts to increase, which is undesirable.

When the hydroisomerization catalyst of this embodiment is used forhydroisomerization of a hydrocarbon oil containing manysulfur-containing compounds and/or nitrogen-containing compounds, it ispreferred that the hydroisomerization catalyst contain, as activemetals, a combination such as nickel-cobalt, nickel-molybdenum,cobalt-molybdenum, nickel-molybdenum-cobalt, or nickel-tungsten-cobaltin view of the persistence of catalytic activity. The amounts of thesemetals supported are preferably 0.001 to 50% by mass based on the massof the support, and more preferably 0.01 to 30% by mass.

In this embodiment, the above-mentioned catalyst precursor is preferablycalcined such that the organic template remaining in the above-mentionedsupport precursor remains. Specifically, heating conditions arepreferably set such that the amount of carbon in the obtainedhydroisomerization catalyst is 0.4 to 3.5% by mass, preferably 0.4 to3.0% by mass, more preferably 0.4 to 2.5% by mass, and the micro-porevolume per unit mass of the catalyst is 0.02 to 0.12 cc/g and themicro-pore volume per unit mass of the zeolite contained in the catalystis 0.01 to 0.12 cc/g. The amount of carbon in the hydroisomerizationcatalyst is measured by “combustion in oxygen gas flow—infraredabsorption method”. Specifically, the catalyst is combusted in theoxygen gas flow to generate carbon dioxide gas and the amount of carbonis determined based on an infrared absorption amount of the carbondioxide gas. Analysis equipments for carbon—sulfur (for example,EMIA-920V manufactured by HORIBA, Ltd.) are used for the measurement.

The micro-pore volume per unit mass of the hydroisomerization catalystis calculated by a method referred to as nitrogen adsorptionmeasurement. That is, the micro-pore volume per unit mass of thecatalyst is calculated by analyzing an isothermal line of nitrogenphysical adsorption and desorption measured at a liquid nitrogentemperature (−196° C.) for the catalyst, and specifically analyzing anisothermal line of nitrogen adsorption measured at a liquid nitrogentemperature (−196° C.) by a t-plot method. The micro-pore volume perunit mass of the zeolite contained in the catalyst is also calculated bythe above-mentioned nitrogen adsorption measurement.

The micro-pore volume V_(Z) per unit mass of the zeolite contained inthe catalyst can be calculated according to the following expressionfrom a value V_(c) of the micro-pore volume per unit mass of thehydroisomerization catalyst and a content ratio M_(z) (% by mass) of thezeolite in the catalyst, for example, when the binder has no micro-porevolume.

V _(z) =V _(c) /Mz×100

It is preferred that, subsequent to the calcination treatment, thehydroisomerization catalyst of the present invention is subjected toreduction treatment, preferably after the catalyst is loaded in thereactor for performing the hydroisomerization reaction. Specifically,the hydroisomerization catalyst is preferably subjected to the reductiontreatment performed for about 0.5 to 5 hours in an atmosphere containingmolecular hydrogen, and preferably under a stream of hydrogen gas,preferably at 250 to 500° C., and more preferably at 300 to 400° C. Thisstep further ensures that high activity for dewaxing a hydrocarbon oilcan be imparted to the catalyst.

An another embodiment of the hydroisomerization catalyst according tothe present invention is a hydroisomerization catalyst that contains asupport containing zeolite having a 10-membered ring one-dimensionalporous structure and a binder, and platinum and/or palladium supportedon the support, wherein the amount of carbon in the catalyst is 0.4 to3.5% by mass, preferably 0.4 to 3.0% by mass, more preferably 0.4 to2.5% by mass, and the micro-pore volume per unit mass of the catalyst is0.02 to 0.12 cc/g, and the above-mentioned zeolite is derived from theion-exchanged zeolite obtained by ion-exchanging organictemplate-containing zeolite containing an organic template and havingthe 10-membered ring one-dimensional porous structure in a solutioncontaining ammonium ions and/or protons, and the micro-pore volume perunit mass of the zeolite contained in the catalyst is 0.01 to 0.12 cc/g.

The above-mentioned hydroisomerization catalyst can be produced by themethod described above. The micro-pore volume per unit mass of thecatalyst and the micro-pore volume per unit mass of the zeolitecontained in the catalyst can be set to the above-mentioned range bysuitably adjusting the mixing amount of the ion-exchanged zeolite in themixture containing the ion-exchanged zeolite and the binder, the heatingconditions of the mixture in the N₂ atmosphere, and the heatingconditions of the catalyst precursor in the atmosphere containingmolecular oxygen.

The peroxide value of the material to be treated subjected to thehydrotreating in the first step is reduced to 30 ppm by mass or less.The material to be treated contains normal paraffins having 10 or morecarbon atoms. In the hydroisomerization in the second step, the materialto be treated may be contacted with the above-mentionedhydroisomerization catalyst in the presence of hydrogen. A portion orentire of the material to be treated containing the normal paraffins isconverted to isoparaffins by the contact with the hydroisomerizationcatalyst.

It is noted that isomerization of the hydrocarbon oil refers to areaction in which only the molecular structure of the hydrocarbon oilchanges without a change in the number of carbon atoms (the molecularweight). It is noted that cracking of the hydrocarbon oil refers to areaction that involves a decrease in the number of carbon atoms(molecular weight) of the hydrocarbon oil. In the catalytic dewaxingreaction utilizing the hydroisomerization catalyst, not only theisomerization but also a certain degree of cracking reaction of thehydrocarbon oil and isomerized products may occur. As long as the numberof carbon atoms (the molecular weight) of the product of the crackingreaction is maintained within a predetermined range that permits theformation of an intended base oil, no problem is caused. That is, thecracked products may also be constituents of the base oil.

The reaction conditions of the hydroisomerization in the second step areas follows.

The temperature of the hydroisomerization reaction is preferably 200 to450° C., and more preferably 220 to 400° C. When the reactiontemperature is below 200° C., the isomerization of the normal paraffinscontained in the material to be treated after the hydrotreating tendsnot to easily proceed, resulting in insufficient reduction and removalof the waxy components. Conversely, when the reaction temperature ismore than 450° C., the cracking of the material to be treated tends tobe significant, to result in a reduced yield of an intended hydrocarbon.

The pressure of the reaction field (in the reactor) in thehydroisomerization reaction is preferably 0.1 to 20 MPa, and morepreferably 0.5 to 15 MPa. When the reaction pressure is below 0.1 MPa,catalyst degradation due to the formation of coke tends to beaccelerated. Conversely, when the reaction pressure is more than 20 MPa,pressure resistance is required for the reactor, and therebyconstruction costs for the reactor tend to increase, to make itdifficult to realize an economical process.

The liquid hourly space velocity of the material to be treated in thehydrotreating reaction is preferably 0.01 to 100 h⁻¹, and morepreferably 0.1 to 50 h⁻¹. When the liquid hourly space velocity is lessthan 0.01 h⁻¹, excessive cracking of the material to be treated tends toeasily proceed, to result in lowered production efficiency for anintended hydrocarbon. Conversely, when the liquid hourly space velocityis more than 100 h⁻¹, the isomerization of the normal paraffinscontained in the material to be treated tends not to easily proceed, toresult in insufficient reduction and removal of the waxy components.

The feed ratio of hydrogen to the material to be treated is preferably100 to 1000 Nm³/m³, and more preferably 200 to 800 Nm³/m³. When the feedratio is less than 100 Nm³/m³, and for example, the material to betreated contains sulfur and nitrogen compounds, hydrogen sulfide andammonia gas produced by desulfurization and denitrification reactionsthat accompany the isomerization reaction tend to adsorb onto and poisonthe active metal on the catalyst. This tends to make it difficult toachieve predetermined catalytic performance. Conversely, if the feedratio is more than 1000 Nm³/m³, hydrogen feed equipment having increasedcapacity tends to be required, which makes it difficult to realize aneconomical process.

The conversion rate of the normal paraffins in the hydroisomerizationreaction is freely controlled by adjusting the reaction conditions suchas the reaction temperature according to the use of the obtainedhydrocarbon.

By the above-mentioned dewaxing method, it is possible to allow theisomerization (i.e., dewaxing) of the normal paraffins contained in theFT wax to proceed, while sufficiently suppressing the conversion of thenormal paraffins to lighter products. Therefore, hydrocarbons containing90% by volume or more of fractions having boiling points of more than360° C. as calculated at ordinary pressure can be produced in highyield.

[Method for Producing Lubricant Base Oil]

In the method for producing a lubricant base oil of the presentinvention, a production oil obtained by the above-mentioned method fordewaxing the hydrocarbon oil is used. According to this embodiment, abase oil having a high content of an isomer having a branched-chainstructure can be obtained. In particular, for a high-quality lubricantbase oil, it is required that the content of normal paraffins is 0.1% bymass or less, however, according to this embodiment, a lubricant baseoil that meets this level of requirement can be obtained in high yield.

When the lubricant base oil is produced, the material to be treatedcontaining normal paraffins having 10 or more carbon atoms is preferablycontacted with the hydroisomerization catalyst in the presence ofhydrogen under conditions that give substantially 100% by massconversion rate of the normal paraffins in the above-mentioned secondstep. Herein, the phrase “substantially 100% by mass conversion rate”means that the content of normal paraffins contained in the material tobe treated after being contacted with the catalyst is 0.1% by mass orless. The conversion rate of the normal paraffins is defined by thefollowing expression (I):

R=(1−M1/M2)×100  (I)

In the expression (I), R is the conversion rate (unit: % by mass) of thenormal paraffins. M1 represents the total mass of the normal paraffinscontained in the material to be treated after being contacted with ahydroisomerization catalyst and having Cn carbon atoms or more. M2represents the total mass of the normal paraffins contained in thematerial to be treated before being contacted with thehydroisomerization catalyst and having Cn carbon atoms or more. Cnrepresents a minimum number of carbon atoms of the normal paraffinscontained in the material to be treated before being contacted with thehydroisomerization catalyst and having 10 or more carbon atoms.

Examples of the above-mentioned method for improving the conversion rateof the normal paraffins include increasing the reaction temperature ofthe hydroisomerization in the second step. Because the content of thenormal paraffins in a reaction product (lubricant base oil) is low whenthe conversion rate is high, the cold flow property of the lubricantbase oil can be improved. However, increasing the reaction temperaturepromotes the cracking reactions of the material to be treated (FT wax)and isomerized products, thereby increasing conversion rate of thenormal paraffins and increasing the amount of light fractions. Becausethe increase in the light fractions decreases the viscosity index of thehydrocarbon oil, in order to maintain the performance of the lubricantbase oil within a predetermined range, it is necessary to separate andremove these light fractions by, for example, distillation. Particularlyin the production of high-performance lubricant base oils such as GroupII (a viscosity index of 80 or more and less than 120, and a saturatedhydrocarbon content of 90% by mass or more, and a sulfur content of0.03% by mass or less), Group III (a viscosity index of 120 or more, anda saturated hydrocarbon content of 90% by mass or more, and a sulfurcontent of 0.03% by mass or less), and Group III+ (a viscosity index of140 or more, and a saturated hydrocarbon content of 90% by mass or more,and a sulfur content of 0.03% by mass or less) according to theclassification of the grades of lubricant oils prescribed by theAmerican Petroleum Institute (API) by catalytic dewaxing of thehydrocarbon feedstock, it is necessary to increase the conversion rateof the normal paraffins up to substantially 100%. With conventionalmethods for producing lubricant base oils using catalysts for catalyticdewaxing, the yields of the above-mentioned high-performance lubricantbase oils are extremely low when dewaxing is performed under conditionsthat give substantially 100% conversion rate. As opposed to this,according to the method for producing a lubricant base oil of thepresent invention, it is possible to increase the yields of theabove-mentioned high-performance lubricant base oils even when thehydroisomerization (second step) is performed under conditions that givesubstantially 100% conversion rate of the normal paraffins.

The reaction equipment for carrying out the first step (hydrotreating)and the reaction equipment for carrying out the second step(hydroisomerization treatment) are not particularly limited. Knownequipment can be used as each equipment. The equipment may be any of acontinuous flow-type, a batch-type, and a semi-batch-type, however, thecontinuous flow-type is preferred in view of productivity andefficiency. The catalyst layer of the equipment may be any of a fixedbed, a fluidized bed, and a stirred bed, however, the fixed bed ispreferred in view of equipment costs or the like. The reaction phase ispreferably a mixed phase of gas and liquid.

This embodiment may comprise the step of subjecting the material to betreated after the hydroisomerization treatment to hydrofinishing. In thehydrofinishing, the material to be treated is contacted with ahydrogenation catalyst supported on a metal, in the presence ofhydrogen. Examples of the hydrogenation catalyst include alumina onwhich platinum is supported. By the hydrofinishing, it is possible toimprove the hue and oxidation stability or the like of the reactionproduct obtained in the dewaxing step (second step), thereby enhancingthe product quality. A catalyst layer for hydrofinishing may be provideddownstream the catalyst layer of the hydroisomerization catalystprovided in the reactor for performing the dewaxing step (second step),and the hydrofinishing may be performed subsequent to the dewaxing step.The hydrofinishing may be carried out in reaction equipment separatefrom that of the dewaxing step. In this embodiment, the material to betreated after the hydrofinishing may be subjected to vacuum distillationto refine the base oil.

EXAMPLES

The present invention will be further described in detail below withreference to Examples, however, the present invention is not limited tothe following Examples as long as Examples do not depart from thetechnical thought of the present invention.

[Production of Catalyst for Hydrotreating]

A mixture of USY zeolite, silica-alumina, and an alumina binder wascylindrically formed by an extrusion method. The mean particle size ofthe USY zeolite was 0.82 μm. The molar ratio of the silica/alumina ofthe USY zeolite was 37. The mass ratio of USY/silica-alumina/aluminabinder in the mixture was 3:47:50. The diameter of the cylinder wasabout 1.5 mm and the length thereof was about 3 mm. The obtainedextruded body was dried and calcined to obtain a support. This supportwas impregnated with an aqueous solution of tetraamminedinitroplatinum[Pt(NH₃)₄](NO₃)₂, to support platinum of 0.6 parts by mass based on themass of the support. This was dried and calcined to obtain a catalystfor hydrotreating for the first step.

[Production of Hydroisomerization Catalyst E-1]

<Synthesis of Organic Template-Containing Zeolite ZSM-22>

Organic template-containing zeolite ZSM-22 made of a crystallinealuminosilicate having a Si/Al ratio of 45 was synthesized in thefollowing procedure. Hereinafter, the zeolite ZSM-22 is referred to asthe “ZSM-22.”

First, the following four types of aqueous solutions were prepared.

Solution A: A solution prepared by dissolving 1.94 g of potassiumhydroxide in 6.75 mL of ion-exchange water.Solution B: A solution prepared by dissolving 1.33 g of aluminum sulfate18-hydrate in 5 mL of ion-exchange water.Solution C: A solution prepared by diluting 4.18 g of 1,6-hexanediamine(an organic template) with 32.5 mL of ion-exchange water.Solution D: A solution prepared by diluting 18 g of colloidal silicawith 31 mL of ion-exchange water. Ludox AS-40 manufactured by GraceDavison was used as the colloidal silica.

Next, the solution A was added to the solution B, and the mixture wasstirred until the aluminum component was completely dissolved. After thesolution C was added to this mixed solution, the mixture of thesolutions A, B, and C was poured into the solution D with vigorousstirring at room temperature. To the resulting mixture, 0.25 g of apowder of ZSM-22 that had been separately synthesized, and had not beensubjected to any special treatment after the synthesis was further addedas a “seed crystal” that promotes crystallization, to obtain a gel.

The gel obtained by the above-mentioned operation was transferred into astainless steel autoclave reactor having an internal volume of 120 mL,and the autoclave reactor was rotated on a tumbling apparatus in aheated oven, to cause a hydrothermal synthesis reaction to take place.The temperature in the oven was 150° C. The execution time of thehydrothermal synthesis reaction was 60 hours. The rotational speed ofthe autoclave reactor was about 60 rpm. After the completion of thereaction, the reactor was opened after cooling, and dried overnight in adrier at 60° C., to obtain ZSM-22 having a Si/Al ratio of 45.

<Ion Exchange of ZSM-22 Containing Organic Template>

The above-mentioned ZSM-22 was subjected to ion-exchange treatment in anaqueous solution containing ammonium ions according to the followingoperation.

The ZSM-22 was taken in a flask, and 100 mL of 0.5 N-ammonium chlorideaqueous solution per gram of the zeolite ZSM-22 was added thereto, andthe mixture was heated under reflux for 6 hours. After cooling theheated mixture to room temperature, the supernatant was removed, and thecrystalline aluminosilicate was washed with ion-exchange water. To theresulting product, the same amount of 0.5 N-ammonium chloride aqueoussolution as above was added again, and the mixture was heated underreflux for 12 hours.

Subsequently, the solids were collected by filtration, washed withion-exchanged water, and dried overnight in a drier at 60° C., to obtainion-exchanged NH₄-form ZSM-22. The ZSM-22 was an ion-exchanged zeolitecontaining an organic template.

<Mixing of Binder, Extruding, and Calcination>

The NH₄-form ZSM-22 obtained above was mixed with alumina as a binder ina mass ratio of 7:3, a small amount of ion-exchange water was addedthereto, and the mixture was kneaded. The obtained viscous fluid wasloaded in an extruder and extruded to obtain a cylindrical extruded bodyhaving a diameter of about 1.6 min and a length of about 10 mm. Thisextruded body was heated in a N₂ atmosphere for 3 hours at 300° C., toobtain a support precursor.

<Supporting of Platinum, and Calcination>

Tetraamminedinitroplatinum [Pt(NH₃)₄](NO₃)₂ was dissolved in an amountof ion-exchange water equivalent to the amount of water absorption ofthe support precursor that had been previously measured, to obtain animpregnation solution. This solution was impregnated in theabove-mentioned support precursor by an incipient wetting method, tosupport platinum on the support precursor such that the amount of theplatinum was 0.3% by mass based on the mass of the zeolite ZSM-22. Next,the obtained impregnation product (catalyst precursor) was driedovernight in a drier at 60° C., and then calcined under an air streamfor 3 hours at 400° C., to obtain a hydroisomerization catalyst E-1containing 0.56% by mass of carbon. The amount of carbon was measured by“combustion in oxygen gas flow—infrared absorption method”. EMIA-920Vmanufactured by HORIBA, Ltd. was used for the measurement.

Furthermore, the micro-pore volume per unit mass of the obtainedhydroisomerization catalyst E-1 was calculated by the following method.First, in order to remove moisture adsorbing onto the hydroisomerizationcatalyst, pretreatment was performed to perform vacuum exhaust at 150°C. for 5 hours. Nitrogen adsorption measurement of thehydroisomerization catalyst after this pretreatment was performed at aliquid nitrogen temperature (−196° C.) using BELSORP-max manufactured byBEL Japan, Inc. The adsorption isothermal line of the measured nitrogenwas analyzed by a t-plot method, to calculate the micro-pore volume(cc/g) per unit mass of the hydroisomerization catalyst. The micro-porevolume per unit mass of the hydroisomerization catalyst was 0.055(cc/g).

Furthermore, the micro-pore volume V_(z) per unit mass of the zeolitecontained in the hydroisomerization catalyst was calculated according tothe expression V_(z)=V_(c)/M_(z)×100. In the expression, V_(c)represents the micro-pore volume per unit mass of the hydroisomerizationcatalyst, and M_(z) represents the content (% by mass) of the zeolite inthe catalyst. When the nitrogen adsorption measurement of alumina usedas the binder was performed as described above, it was confirmed thatalumina does not have micropores. The micro-pore volume V_(z) was 0.079(cc/g).

[Production of Hydroisomerization Catalyst E-2]

<Synthesis of Organic Template-Containing Zeolite ZSM-48>

Organic template-containing zeolite ZSM-48 having a Si/Al ratio of 45was synthesized in the following procedure. Hereinafter, the zeoliteZSM-48 is referred to as the “ZSM-48.”

First, the following five types of reagents were prepared.

Reagent A: 2.97 g of sodium hydroxide.Reagent B: 0.80 g of aluminum sulfate 18-hydrate.Reagent C: 26.2 g of 1,6-hexanediamine (organic template).Reagent D: 0.9 ml of a 98% sulfuric acid solution.Reagent E: 75 g of a colloidal silica aqueous solution (SiO₂concentration: 40%). Ludox AS-40 manufactured by Grace Davison was usedas the colloidal silica.

The above-mentioned reagents A, B, C, D, and E were added to 180 mg ofion-exchange water, and then completely dissolved by stirring for 2hours at normal temperature.

The gel obtained by the above-mentioned stirring operation wastransferred into a 100 mL internal volume stainless steel autoclavereactor, and the autoclave reactor was rotated on a tumbling apparatusin a heated oven, to cause a hydrothermal synthesis reaction to takeplace. The temperature in the oven was 160° C. The execution time of thehydrothermal synthesis reaction was 60 hours. The rotational speed ofthe autoclave reactor was about 60 rpm. After the completion of thereaction, the reactor was opened after cooling, and dried overnight in adrier at 60° C., to obtain ZSM-48 having a Si/Al ratio of 45.

<Ion Exchange of ZSM-48 Containing Organic Template>

The inn-exchange treatment of 7KM-48 was performed according to the sameoperation as that in the case of the catalyst E-1 except that the ZSM-48was used instead of the ZSM-22. Ion-exchanged NH₄-form ZSM-48 wasobtained by this treatment. The ZSM-48 was an ion-exchanged zeolitecontaining an organic template.

A series of steps including mixing of the binder, extruding, calcining,supporting of platinum, and calcining were carried out in the samemanner as in the catalyst E-1 except that the NH₄-form ZSM-48 was used,to obtain a hydroisomerization catalyst E-2, wherein the amount ofcarbon in the hydroisomerization catalyst is 0.43% by mass, and themicro-pore volume per unit mass of the hydroisomerization catalyst is0.078 cc/g, and the micro-pore volume per unit mass of the zeolitecontained in the hydroisomerization catalyst is 0.111 cc/g.

[Production of Hydroisomerization Catalyst E-3]

<Synthesis of Organic Template-Containing Zeolite SSZ-32>

Organic template-containing zeolite SSZ-32 was synthesized in thefollowing procedure. Hereinafter, the zeolite SSZ-32 is referred to asthe “SSZ-32.”

Sodium hydroxide, aluminium sulfate, colloidal silica, isobutylamine(organic template), and an N-methyl-N-isopropyl-imidazolium cation weremixed to give the following molar ratios, and prepared:

SiO₂/Al₂O₃=35.

The total amount (unit: g) of the isobutylamine andN-methyl-N′-isopropyl-imidazolium cation was 0.2 times the amount ofSiO₂.

The gel obtained by the above-mentioned operation was transferred into a100 mL internal volume stainless steel autoclave reactor, and theautoclave reactor was rotated on a tumbling apparatus in a heated oven,to cause a hydrothermal synthesis reaction to take place. Thetemperature in the oven was 160° C. The execution time of thehydrothermal synthesis reaction was 60 hours. The rotational speed ofthe autoclave reactor was about 60 rpm. After the completion of thereaction, the reactor was opened after cooling, and dried overnight in adrier at 60° C., to obtain SSZ-32 having a Si/Al ratio of 45.

<Ion Exchange of SSZ-32 Containing Organic Template>

The ion-exchange treatment of SSZ-32 was performed according to the sameoperation as that in the case of the catalyst E-1 except that the SSZ-32was used instead of the ZSM-22. Ion-exchanged NH₄-form SSZ-32 wasobtained by this treatment. The SSZ-32 was an ion-exchanged zeolitecontaining an organic template.

A series of steps including mixing of the binder, extruding, calcining,supporting of platinum, and calcining were carried out in the samemanner as in the catalyst E-1 except that NH₄-form SSZ-32 was used, toobtain a hydroisomerization catalyst E-3, wherein the amount of carbonin the hydroisomerization catalyst is 0.50% by mass, and the micro-porevolume per unit mass of the hydroisomerization catalyst is 0.062 cc/g,and the micro-pore volume per unit mass of the zeolite contained in thehydroisomerization catalyst is 0.089 cc/g.

Example 1 First Step

An FT synthetic oil was obtained using an FT synthesis reactor. Thereaction temperature of an FT reaction was 210° C. A crude wax (FT wax)was obtained by the fractionation of the FT synthetic, oil. Componentsconstituting the FT wax, and the content thereof were as follows.

Alcohols: 3.3% by mass.Normal paraffin: 92.5% by mass.Olefins: 4.2% by mass.

This crude wax was transported to a hydrotreating apparatus that was notadjacent to the FT synthesis reactor from the FT synthesis reactorwithout being treated. The peroxide value of the transported crude waxwas measured by the following method.

The peroxide value was measured by reacting hydroperoxide in the crudewax with potassium iodide, and titrating free iodine with a sodiumthiosulfate solution. The specific procedure of the measurement was asfollows. First, the crude wax was precisely measured off. A liquidmixture of chloroform and glacial acetic acid (volume ratio 2:3) wasadded into the crude wax put into a stoppered Erlenmeyer flask, todissolve the crude wax. Subsequently, while air in the flask wasreplaced by inactive gas, a saturated potassium iodide solution wasadded into the liquid mixture in which the crude wax was dissolved, anda stopper was immediately closed. After the liquid mixture in the flaskwas mixed for several minutes, a starch test solution as an indicatorwas added into the liquid mixture, and iodine in the liquid mixture wastitrated with the sodium thiosulfate solution.

The peroxide value of the crude wax measured by the above-mentionedmethod was 430 ppm by mass.

[First Step: Hydrotreating]

The transported crude wax was subjected to hydrotreating using ahydrotreating apparatus. In the hydrotreating, the crude wax wascontacted with the above-mentioned catalyst for hydrotreating in ahydrogen gas flow. The conditions of the hydrotreating were as follows.

A reaction temperature of hydrotreating: 290° C.A reaction pressure of hydrotreating: 4.0 MPa.A hydrogen/crude wax ratio: 340 Nm³/m³.LHSV of crude wax: 2.0 h⁻¹.

Generally, in the hydrotreating, the catalyst for hydrotreating isdegraded with elapse of time to reduce a cracking rate. Therefore, inthe above-mentioned hydrotreating, the reaction temperature was stepwiseand continuously increased from 290° C. such that the cracking raterepresented by the following expression (II) was maintained at 30%, tocompensate for the reduced catalytic activity. The cracking rate wascalculated from the analysis result of a production oil by a gaschromatography method. The upper limit value of the reaction temperaturewas set to 350° C. The temperature of 350° C. is a temperature at whichpolycyclic aromatic hydrocarbons are generated in the production oil ofthe hydrotreating to start to cause the degradation of the hue of theproduction oil. If the reaction temperature is increased to atemperature higher than 350° C. in order to compensate for the catalyticactivity, the hue of the production oil is worsened to reduce thequality of the base oil product obtained from the production oil. Thatis, at the reaction temperature more than 350° C., it becomes difficultto satisfy both the compensation of the catalytic activity and theprevention of the degradation of the hue.

Cracking rate (% by mass)=Ma/Mb×100  (II)

Ma: the mass of a fraction contained in the production oil of thehydrotreating and having a boiling point of less than 360° C.Mb: the mass of a fraction contained in the crude wax and having aboiling point of 360° C. or more.

A time t1 required to increase the reaction temperature of thehydrotreating to 350° C. from 290° C. was measured. The time t1 ofExample 1 was 730 days. The short time t1 means that the catalyst isdegraded in a short time. Therefore, the time t1 means the life of thecatalyst for hydrotreating.

The production oil obtained by the hydrotreating of the crude wax wasdistilled, to obtain a fraction having a boiling point of 520° C. orless under ordinary pressure. A fraction having a boiling point of 520°C. or more was mixed with an FT production oil, and subjected to thehydrotreating again.

The peroxide value of the production oil (material to be treated)obtained by the above-mentioned hydrotreating was measured by the samemethod as the case of the crude wax before the hydrotreating. Theperoxide value of the production oil of Example 1 was 0 ppm by mass.

[Second Step: Hydroisomerization Treatment]

The production oil of Example 1 was subjected to hydroisomerizationtreatment (dewaxing treatment) using a hydroisomerization catalystaccording to the following procedure.

The above-mentioned catalyst E-1 was used as the hydroisomerizationcatalyst. Before the hydroisomerization treatment is performed, thecatalyst E-1 was subjected to the following pretreatment. Astainless-steel reaction tube having an inner diameter of 15 mm and alength of 380 mm was loaded with 100 ml of the catalyst E-1. Thecatalyst E-1 in the reaction tube was subjected to reduction treatmentfor 12 hours under a hydrogen stream. In the reduction treatment, theaverage temperature of the catalyst layer (catalyst E-1) in the reactiontube was adjusted to 350° C. The hydrogen partial pressure in thereaction tube was adjusted to 3 MPa.

The production oil of Example 1 in which the peroxide value wasmaintained at 0 ppm by mass was passed in the above-mentioned reactiontube after the reduction treatment, to subject the production oil to thehydroisomerization treatment. The reaction temperature of thehydroisomerization was adjusted to the range of 310 to 330° C. Thehydrogen partial pressure in the reaction tube during thehydroisomerization was adjusted to 3 MPa. LHSV of the production oilintroduced into the reaction tube was adjusted to 1.0 h⁻¹. Ahydrogen/production oil ratio was adjusted to 500 Nm³/m³. The reactiontime of the hydroisomerization was 72 hours. The hydroisomerizationproduct was collected and analyzed.

Subsequently, the hydrogen partial pressure, the LHSV, and thehydrogen/production oil ratio were maintained at the above-mentionedvalues, and the reaction temperature was increased stepwise to about350° C., to increase the conversion rate of the normal paraffins asdefined by the above-mentioned expression (I). That is, at a pluralityof reaction temperatures, the hydroisomerization reactions were causedto proceed. After the hydroisomerization reaction was continued at eachreaction temperature for 72 hours and the reaction product wasstabilized, the reaction product was collected and analyzed. Theconversion rate of the normal paraffins in the hydroisomerization ateach reaction temperature was calculated using the above-mentionedexpression (I) based on the analysis result.

[Separation and Recovery Steps of Lubricant base oil Fractions]

Of the reaction products of the hydroisomerization treatment at thereaction temperatures, each of the reaction products obtained atreaction temperatures at which the conversion rate of the normalparaffins was 100% was fractionated according to the followingoperation. The following lubricant base oil fractions were separated andrecovered by the fractionation.

Each of the reaction products obtained at reaction temperatures at whichthe conversion rate of the normal paraffins was 100% was fractionatedinto naphtha, kerosene and gas oil fractions, and heavy fractions. Theheavy fractions were further fractionated into a lubricant base oilfraction 1 and a lubricant base oil fraction 2. The lubricant base oilfraction 1 means a lubricant base oil fraction having a boiling pointrange of 330 to 410° C. and having a kinematic viscosity at 100° C. of2.7±0.1 mm²/s. The lubricant base oil fraction 2 means a lubricant baseoil fraction having a boiling point range of 410 to 450° C. and having akinematic viscosity at 100° C. of 4.0±0.1 mm²/s.

The lowest initial reaction temperature in the reaction temperatures ofthe hydroisomerization at which the lubricant base oil fraction 2 havinga pour point of −22.5° C. or less and a viscosity index (VI) of 140 ormore was generated was defined as Tc (° C.). The reaction temperature Tcof the hydroisomerization treatment of Example 1 was 325° C. Table 1shows the yields of the lubricant base oil fractions 1 and 2 obtained bythe hydroisomerization treatment at the reaction temperature Tc, and thepour point and viscosity index of the lubricant base oil fraction 2.

[Life Evaluation of Hydroisomerization Catalyst]

Generally, in the hydroisomerization treatment, the hydroisomerizationcatalyst is degraded with elapse of time to decrease the conversion rateof the normal paraffins. Therefore, in the hydroisomerization treatmentin which the initial reaction temperature was Tc, the reactiontemperature was gradually and continuously increased to 350° C. from Tcsuch that the conversion rate of the normal paraffins was maintained at100%, to compensate for the reduced catalytic activity. The conversionrate was calculated from the analysis result of the reaction product ofthe hydroisomerization treatment by the gas chromatography method. Atime t2 required to increase the reaction temperature of thehydroisomerization treatment to 350° C. from Tc was measured. The timet2 of Example 1 was 670 days. The short time t2 means that the catalystis degraded in a short time. Therefore, the time t2 means the life ofthe hydroisomerization catalyst.

Example 2

In Example 2, in a second step, not the catalyst E-1 but the catalystE-2 was used as a hydroisomerization catalyst. In the same manner as inExample 1 except for this point, hydrotreating, hydroisomerizationtreatment, and separation and recovery steps of a lubricant base oilfraction of Example 2 were performed. A peroxide value of a crude waxbefore the hydrotreating, a catalyst life t1, a peroxide value of aproduction oil (material to be treated) obtained by the hydrotreating, areaction initial temperature Tc, yields of lubricant base oil fractions1 and 2, a pour point and viscosity index of the lubricant base oilfraction 2, and a catalyst life t2 in Example 2 were obtained in thesame manner as in Example 1. These are shown in Table 1.

Example 3

In Example 3, in a second step, not the catalyst E-1 but the catalystE-3 was used as a hydroisomerization catalyst. In the same manner as inExample 1 except for this point, hydrotreating, hydroisomerizationtreatment, and separation and recovery steps of a lubricant base oilfraction of Example 3 were performed. A peroxide value of a crude waxbefore the hydrotreating, a catalyst life t1, a peroxide value of aproduction oil (material to be treated) obtained by the hydrotreating, areaction initial temperature Tc, yields of lubricant base oil fractions1 and 2, a pour point and viscosity index of the lubricant base oilfraction 2, and a catalyst life t2 in Example 3 were obtained in thesame manner as in Example 1. These are shown in Table 1.

Comparative Example 1

In Comparative Example 1, an FT synthetic oil was produced using an FTsynthesis reactor set in a GTL plant apart from Example 1. A crude waxwas obtained by the fractionation of the FT synthetic oil. The peroxidevalue of the crude wax of Comparative Example 1 was measured in the samemanner as in Example 1. The peroxide value of the crude wax ofComparative Example 1 was 2420 ppm by mass. This crude wax was subjectedto hydrotreating under the same reaction conditions as those ofExample 1. The life t1 of a catalyst for hydrotreating of ComparativeExample 1 was measured in the same manner as in Example 1. The life t1of the catalyst for hydrotreating of Comparative Example 1 was 135 days.

A production oil (material to be treated) obtained by the hydrotreatingwas transported to a reaction tube for hydroisomerization treatment usedin Example 1 from the GTL plant. The transporting period was two months.The peroxide value of the production oil after the transportation (justbefore hydroisomerization treatment) was measured in the same manner asin Example 1. The peroxide value of the production oil after thetransportation of Comparative Example 1 was 34 ppm by mass.

The hydroisomerization treatment and the separation and recovery stepsof a lubricant base oil fraction of Comparative Example 1 were performedin the same manner as in Example 1 except for the above matters. Areaction initial temperature Tc, yields of lubricant base oil fractions1 and 2, a pour point and viscosity index of the lubricant base oilfraction 2, and a catalyst life t2 in Comparative Example 1 wereobtained in the same manner as in Example 1. These are shown in Table 1.

Comparative Example 2

In Comparative Example 2, an FT synthetic oil was produced using an FTsynthesis reactor set in a GTL plant apart from Example 1 andComparative Example 1. A crude wax was obtained by the fractionation ofthe FT synthetic oil. The peroxide value of the crude wax of ComparativeExample 2 was measured in the same manner as in Example 1. The peroxidevalue of the crude wax of Comparative Example 2 was 3700 ppm by mass.This crude wax was subjected to hydrotreating under the same reactionconditions as those of Example 1. The life t1 of a catalyst forhydrotreating of Comparative Example 2 was measured in the same manneras in Example 1. The life t1 of the catalyst for hydrotreating ofComparative Example 2 was 93 days.

A production oil (material to be treated) obtained by the hydrotreatingwas transported to a reaction tube for hydroisomerization treatment usedin Example 1 from the GTL plant. The transporting period was fourmonths. The peroxide value of the production oil (material to betreated) after the transportation was measured in the same manner as inExample 1. The peroxide value of the production oil after thetransportation (just before hydroisomerization treatment) of ComparativeExample 2 was 128 ppm by mass.

The hydroisomerization treatment and the separation and recovery stepsof a lubricant base oil fraction of Comparative Example 2 were performedin the same manner as in Example 1 except for the above matters. Areaction initial temperature Tc, yields of lubricant base oil fractions1 and 2, a pour point and viscosity index of the lubricant base oilfraction 2, and a catalyst life t2 in Comparative Example 2 wereobtained in the same manner as in Example 1. These are shown in Table 1.

In the following Table 1, a “peroxide value 1” means the peroxide valueof the crude wax before the hydrotreating. The “life t1” means the lifeof the catalyst for hydrotreating in the hydrotreating of the crude wax.A “peroxide value 2” means the peroxide value just before thehydroisomerization treatment of the production oil obtained by thehydrotreating. The “catalyst” means a hydroisomerization catalyst. The“life t2” means the life of the hydroisomerization catalyst in thehydroisomerization treatment of the production oil.

Table 1 Peroxide Peroxide Fraction 2 value 1 Life value 2 Life Yield (%)Pour (ppm by t1 (ppm by Tc t2 Fraction Fraction point Viscosity Table 1mass) (day) mass) Catalyst (° C.) (day) 1 2 (° C.) index Example 1 430730 0 E-1 325 670 30 62 −27.5 148 Example 2 430 730 0 E-2 320 660 34 57−25.0 145 Example 3 430 730 0 E-3 325 640 30 57 −27.5 148 Comparative2420 135 34 E-1 327 600 39 62 −27.5 148 Example 1 Comparative 3700 93128 E-1 330 520 28 63 −27.5 148 Example 2

INDUSTRIAL APPLICABILITY

Because the present invention improves the life of thehydroisomerization catalyst and enables effective hydroisomerizationtreatment (dewaxing treatment) of the hydrocarbon oil at low cost, thepresent invention is suitable for the method for producing the lubricantbase oil or the like.

1. A method for dewaxing a hydrocarbon oil comprising: a first step ofsubjecting a hydrocarbon oil in which a peroxide value is 100 ppm bymass or more to hydrotreating to obtain a material to be treated inwhich a peroxide value is 30 ppm by mass or less; and a second step ofsubjecting the material to be treated in which a peroxide value is 30ppm by mass or less to hydroisomerization treatment using ahydroisomerization catalyst.
 2. The method for dewaxing a hydrocarbonoil according to claim 1, wherein the hydrocarbon oil is synthesized bya Fischer-Tropsch reaction.
 3. The method for dewaxing a hydrocarbon oilaccording to claim 1, wherein the hydroisomerization catalyst containszeolite; and the zeolite contains an organic template, and has aone-dimensional porous structure including a 10-membered ring.
 4. Themethod for dewaxing a hydrocarbon oil according to claim 3, wherein thezeolite is at least one selected from the group consisting of zeoliteZSM-22, zeolite ZSM-23, zeolite SSZ-32, and zeolite ZSM-48.
 5. Themethod for dewaxing a hydrocarbon oil according to claim 1, wherein thematerial to be treated contains normal paraffins having 10 or more ofcarbon number; and the material to be treated is contacted with thehydroisomerization catalyst in the presence of hydrogen in the secondstep.
 6. A method for producing a lubricant base oil using the methodaccording to claim
 1. 7. The method for producing a lubricant base oilaccording to claim 6, further comprising a step of subjecting thematerial to be treated after the hydroisomerization treatment tohydrofinishing.
 8. The method for producing a lubricant base oilaccording to claim 7, further comprising a step of subjecting thematerial to be treated after the hydrofinishing to vacuum distillation.